Tomosynthesis is used to reconstruct a three-dimensional image of a person's body part, for example a breast in a mammography examination. The typical arrangement for creating such images require that the focal spot of an x-ray source (104, 204, 304) is allowed to rotate in relation to an object (108, 208, 308) such as a breast, whereby an interval of projection angles through each location in the object (108, 208, 308) is scanned creating individual projection images for each projection angle. With data comprising a multitude of 2D projection images, reconstruction into a 3D image is possible using computers running algorithms including back-projection as a computational step. Examples of algorithms are filtered back projection, algebraic reconstruction and Lange-Fessler Convex algorithm from 1995. Examples x-ray imaging apparatuses enabling the construction of tomosynthesis images are for instance U.S. Pat. No. 7,302,031 and U.S. Pat. No. 6,496,557.
In prior art, x-ray systems with the capability of creating projection angles, i.e. tomo-angles, has been proposed. Generally, such solutions allow either a linear or rotational movement of the x-ray source (104, 204, 304) in relation to the detector (105, 205, 305) and the object (108, 208, 308) to be scanned, wherein the detector (105, 205, 305) may also be adapted to be movable in a linear or rotational manner. It has been proposed to allow for the creation of both 2D images, wherein the x-ray source (104, 204, 304) is stationary and the detector (105, 205, 305) rotates around the x-ray source (104, 204, 304) and the investigated object, and 3D tomosynthesis images, wherein the x-ray source (104, 204, 304) is movable in relation to the detector (105, 205, 305) and the investigated object, in the same system. Examples of such systems can for instance be found in U.S. Pat. No. 7,302,031 and U.S. Pat. No. 6,496,557.
X-ray systems as described in the prior art with the capacity to generate variable tomosynthesis images requires heavier systems and preferably more complex scan motions with more degrees of freedom than traditional 2D x-ray imaging systems in order to achieve the sought after projection angles and images. However, the scan movement during a mammography investigation of such systems is set by an operator based on preset movement schemes. This will have a negative implication on the image quality as the most optimal projection angles are not achieved for each object (108, 208, 308) that is scanned, concerning for instance the size, thickness and other characteristics of the object. Further, such systems does not have the ability to prevent certain scan movements that should be avoided based on characteristics of the object that is scanned in a direct or indirect manner.
Further, the solutions in the prior art does not describe an adaptive controlling of the scan movement wherein external data is taken into account in order to optimize the tomo-angles during a scan of an object.
In prior art shielding apparatuses used in mammography applications it has been proposed to use box or telescopic shielding means for protecting the patient and operator against scatter. Such exemplary prior art can for instance be seen in EP1480560 B1 which discloses scanning apparatus wherein the x-ray source is fixed during the scanning movement. The shielding means herein is automatically installed in a vertical direction based upon the installment of the patient breast support which height is based on the size of the object to be scanned. The purpose of such solutions are to prevent scattered radiation, not to prevent the direct radiation that does not add to the generation or improvement of an image of a scanned object.
In prior art it has been proposed to use a position encoder in an x-ray imaging system to synchronize the receiver readout with the scanning motion so as to yield a high fidelity composite 2D image. Herein the encoders are used to produce signals as a function of detector array motion, wherein these signals are used to trigger charge shifting across an array of pixels. Since the charge shifting is referenced to encoder output, synchronization is maintained despite variances in drive speed or due to other irregularities.
In other prior art documents, tomosynthesis is a method used to reconstruct a three-dimensional image of a person's body part, for example a breast in a mammography examination. The typical arrangement for creating such images requires that the focal spot of an x-ray source is allowed to move in relation to an object such as a breast, whereby an interval of projection angles through each location in the object is scanned creating individual projection images for each projection angle. With data comprising a multitude of 2-dimensional projection images, reconstruction into a 3D image is possible using computers running reconstruction algorithms involving so-called back-projection as a computational step. Examples of documents disclosing x-ray imaging apparatuses enabling the construction of tomosynthesis images are for instance U.S. Pat. No. 7,302,031 and U.S. Pat. No. 6,496,557.
Tomosynthesis scanners with variable scan motions require heavier systems and preferably more complex scan motions with more degrees of freedom than traditional x-ray imaging systems in order to achieve and optimize the projection angles and images. However, the reconstruction of 3D images requires a precision in the scan motion in order not to cause motion blur in the reconstructed image which is non-compliant to the heavy systems described in which play is prone to develop over time, for instance in various actuation mechanisms that are used for controlling the movement of a certain scan, as well as due to the motors controlling the scan motion which are not possible to control in a perfect manner. In order to obtain precise image quality without artifacts resembling motion blur, prior art may have to rely on expensive movement control systems and motors, and force transmission without backlash or deflection.